The tank does seem pretty close. Sadly that ball I can't find anywhere either. Its all the newer tanks i keep seeing. I did come across the Hammer Blue Vibe RG (2.51) Diff (0.039. So that might end up being the one if I can't find an actual U2 or Original Tank.

Blue Vibe is reactive, so with you looking for a urethane ball, it will not fit. The core numbers are close, yes, but the cover is what dictates the motion. I think the Black Hammer will be the closest current choice.